Wireless communication systems are widely used to provide voice and data services for multiple users using a variety of access terminals such as cellular telephones, laptop computers and various multimedia devices. Such communications systems can encompass local area networks, such as IEEE 801.11 networks, cellular telephone and/or mobile broadband networks. The communication system can use one or more multiple access techniques, such as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA) and others. Mobile broadband networks can conform to a number of standards such as the main 2nd-Generation (2G) technology Global System for Mobile Communications (GSM), the main 3rd-Generation (3G) technology Universal Mobile Telecommunications System (UMTS) and the main 4th-Generation (4G) technology Long Term Evolution (LTE).
As technologies evolve, different generation standards may co-exist in a wireless network for a period. For example, when a wireless device user moves from one region covered by GSM to another region covered by UMTS, the user demands a seamless handover between two standards. Such a seamless handover requires a multi-mode wireless device. On the other hand, in specific regions of the world, each standard may operate within different frequency bands. In order to accommodate different frequency bands in a wireless system, the wireless device must have a multi-band communication capability. In short, a modern wireless device such as a mobile phone must be a multi-band and multi-mode device.
Each wireless standard may have different frequency bands. For example, GSM may operate on frequency bands in a range around 850 Megahertz (MHz), 900 MHz, 1800 MHz and 1900 MHz. Similarly, UMTS may operate on even diversified frequency bands in a range from low 800 MHz up to 2200 MHz. CDMA may operate on frequency bands in a range around 850 MHz and 1900 MHz. LTE may support both future and existing frequency bands used by current 3G systems. In consideration of the antenna design of a wireless device, frequency bands around 850 MHz and 900 MHz are defined as a low-band frequency. Likewise, frequency bands above 1700 MHz are defined as a high-band frequency.
A wireless device capable of operating in multi-band frequencies may have at least two antennas so that both high-band frequency signal and low-band frequency signal reception/transmission can be optimized. For example, when a mobile phone is operating in a wireless system having both GSM bands and UMTS bands, it has one primary antenna and one secondary antenna. The primary antenna usually has a higher efficiency than the secondary antenna. Traditionally, some important signals such as transmitted signals and primary received signals are connected to the primary antenna to achieve best performance. However, as more and more access techniques are deployed, the existing primary-secondary antenna architecture may not deliver the highest performance for all frequency bands. Therefore, there is an ever increasing pressure to improve the performance of these two antennas.